Just for some more info, guest advanced downsampling on y-axis “always” does integer level resolution reduction in an integer value (greater than 0.0) is selected.
It’s fitting the situation almost every time, especially when a core supports internal resolution multiplying.
There are also possible values like “3.5”, a plausible option with some cores like N64, which operate at selected original resolutions (i.e. 800x600, 1024x768…) instead.
With the mentioned DOS game using “1.0” parameter value does a smart integer resolution divider, which favours certain scanline resolutions (based around 200-240). Specific scanline resolution isn’t forced, but specific integer divider instead.
If a game runs in 640x480, then downsampling to 240px is probably the only reasonable option. If vertical pixel information gets discarded in the process, then there are interpolation options for both x and y axsis, which add the flavour of quality downsampling.